# REDUCTION OF LINE LOSSES, VOLTAGE STABILIZATION, POWER FACTOR - Download Now DOC

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```					 Course # (EE6723) Power Quality

Supervisor: Professor: Dr. A.M Sharaf (P.Eng)

By

Pierre Kreidi

Student ID # 205475

ECE Department

University of New Brunswick

Page 1 of 58
CONTENTS

Summary………………………………………………………………………………..4
1.       Background………………………………………………………………………… …5
2.       Why Are we concerned about Power Quality…………........................................7
3.       Power Quality Issues and Problem Formulation…………………………………...8
4.       Total Harmonic Distortion and Power Factor……………………………………….9
5.       Power Quality Disturbances………………………………………………………….10
5.1    Short duration voltage variations…………………………………………………..11
5.1.1   Sag………………………………………………………………………………… ………11
5.1.2   Swell………………………………………………………………………………… ……..12
5.1.3   Interruption…………………………………………………………………………..…….13
5.2       Long duration voltage variations………………………………………………..…..13
5.2.1   Overvoltage…………………………………………………………………………….….13
5.2.2   Undervolt age……………………………………………………………………………....14
5.3       Transients……………………………………………………………………………..14
5.3.1   Impulsive Transient……………………………………………………………………….14
5.3.2   Oscillatory Transient………………………………………………………………………14
5.4       Voltage imbalance……………………………………………………………………16
5.5       Waveform distortion…………………………………………………………………..17
5.5.1   DC offset……………………………………………………………………………………17
5.5.2   Harmonic……………………………………………………………………………………17
5.5.3   Interharmonics……………………………………………………………………………..18
5.5.4   Notching……………………………………………………………………………………..19
5.5.5   Noise…………………………………………………………………………………………19
5.6   Voltage Fluctuation……………………………………………………………………19
5.7   Power Frequency variations………………………………………………………...20
6.     Reactive Power Problems…………………………..................................................20
6.1     Reactive power sources………………………………………………………………21
6.1.1 Generators…………………………………………………………………………21
6.1.2 Power Transfer Components……………………………………………………22
6.1.2.1 Trans formers…………………………………………………………………………..22
6.1.2.2 Transmission Lines and Cables……………………………………………………..23
6.1.2.3 HVDC Converters……………………………………………………………………..24
6.1.3   Loads……………………………………………………………………………….24
6.1.3.1   Induction mot ors……………………………………………………………………….24
6.1.3.2   Induction generat ors………………………………………………………………….25
6.1.3.3   Discharge lightning…………………………………………………………………….25
6.1.3.4   Constant energy loads…………………………………………………………..……25
6.1.3.5   Arc furnaces………………………………………………………………………..…..26
6.1.4   Reactive Power Compensation Devices…………………………………..……26
6.1.4.1   Synchronous condensers……………………………………………………..………26
6.1.4.2   Static VAR compensators………………………………………………….…………27
6.1.4.3   Harmonic Filter…………………………………………………………………….…..27
6.1.4.4   Static synchronous compensators………………………………………………….28
6.1.4.5   Series capacitors and reactors……………………………………………………..29
6.1.4.6   Shunt capacitors……………………………………………………………………..29
6.1.4.7   Shunt reactors………………………………………………………………………..30
6.1.5 Why Power factor Correction…………………………………………………..30
6.1.5.1 Power factor correction techniques………………………………………..30

Page 2 of 58
7.       Software……………………………………………………………………………….31
8.       Digital Simulation Models……………………………………………………………31
8.1     System models…………………………………………………………………...32
8.1.1 Cases # 1 to Case # 5……………………………………………………….33
Case # 1……………………………………………………………………….33
Case # 2………………………………………………………………………..33
Case # 3………………………………………………………………………..34
Case # 4………………………………………………………………………..34
Case # 5………………………………………………………………………..35

References……………………………………………………………………………………………36
Appendix ‘A’…………………………………………………………………………………………..38
Appendix ‘B’…………………………………………………………………………………………..43
Appendix ‘C’…………………………………………………………………………………………..47
Appendix ‘D’…………………………………………………………………………………………..53
Appendix ‘E’…………………………………………………………………………………………..55

Page 3 of 58
Summary

This Project comprises of 5 separate cases of Power Quality, Reactive Power and Modulated
Power Filter Compensators. These cases have been modulated with and without
compensation devices and have been simulated using both Matlab/Simulink and PSCAD
software.
The 5 cases are as follows:
1.       Power Quality Enhancement Using Modulated Power Filter
2.       Power Quality Enhancement and Voltage regulation Using Modulated Power Filter
3.       Power Quality Enhancement Using STATCOM
4.       Power Quality Enhancement addressing the Tingle Voltage Issue
5.       Power Quality Enhancement and Voltage regulation Using STATCOM

Detail information about the cases and digital simulation are shown under section 8.1.1 and
under the Appendices A to E.

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1. Background
The research course project EE6723 addresses the current issues of Electric Power

Supply Pollution, Power Quality (PQ) and Harmonic Distortion Problems. The term

“Power Quality” is in general a broad concept and is associated with electrical

distribution and utilization systems that experience any voltage, current or frequency

deviation from normal operation. For ideal electrical systems, the supplied power should

have perfect current and voltage sinusoidal waveforms, being safe and reliable. But the

reality is that the electric utilities controls the voltage levels and quality but are unable to

control the current, since the load profile dictates the shape of the current waveform.

Thus, the utility should maintain the bus voltage quality at all times. This simple

consideration makes power quality (PQ) equal to voltage quality as shown in Figure 1.1

Defining precisely the Power Quality is a tremendous task; one of the common

definitions is:

Definition 1: “Power quality is a summarizing concept, includi ng different criteria to

Judge the technical quality of an electric power delivery”.             Another definition is

developed and adopted by Ontario Hydro:

Definition 2: “Power Quality is the degree to which both the utilization and delivery of

electric power affects the performance of electric equipment”.

In general there is no unique definition of power quality. The power quality problem can

be viewed from two different angles related to each side of the utility meter, namely the

Utility and the Consumer. An alternative definition of PQ is adopted:

Definition 3: “Power quality problem is any power problem manifested in voltage,

current, or frequency deviation that results in failure or misoperation of customer

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equipment”. Power quality can be simply defined as shown in the interaction diagram

Figure 1.1

Electrical Grid
Utility

Voltage         Current                Power
Quality         Quality                Quality

Loads
Consumers

Figure 1.1: The Power Quality Diagram

Delivering a certain level of voltage stability and sinusoidal quality should be the

main    concern     for   designers   of    the   utility    electrical   grid.   When   electrical

distribution/utilization system is interconnected, electric loads and their profile, grid

design, utility operation including the electric load degree of nonlinearity, all together

affect and influence the power quality.

An important article appeared in the Electrical Business Magazine in December 2001

quoted Ms Jane Clemmensen, a well-known power quality authority in Berkerly,

California, “as every year, North American industries lose Tens -of-Billions of Dollars in

downtime due to electric faults in the quality of electric power delivered to factories and

other industrial facilities”.

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2. Why Are We Concerned With Power Quality
Power Quality (PQ) has caused a great concern to electric utilities with the growing use

of sensitive and susceptive electronic and computing equipment (e.g. personal

computers, computer-aided design workstations, uninterruptible power supplies, fax

machines, printers, etc) and other nonlinear loads (e.g. fluorescent lighting, adjustable

speed drives, heating and lighting control, industrial rectifiers, arc welders, etc).    All

nonlinear and time varying temporal type electric loads fall generally in two wide

categories, namely the analog arc (inrush/saturation) type and digital converter (power

electronic) switching type. The Electric Power Research Institute (EPRI) gives a rough

estimation that in 1992, 15 to 20% of the total electric utility load was nonlinear and this

trend in rising and is expected to reach 50 to 70% in the year 2000.

The reasons behind the growing concern about power quality are:

   The characteristics of the electric loads have changed dramatically with the

proliferation of new microelectronics and sensitive computer type equipment.

   Harmonics cause equipment to fail prematurely and also decrease the efficiency

of the electric distribution/utilization network.

   Electric power systems are now interconnected, integrated, and thus any system

disturbance can have an extended serious economic impact particularly for large

industrial type consumers due to process shutdown.

   Deregulation of the electricity market. Consumers are now much more aware of

the PQ problems issues, and its effect on equipment failure and safety hazards.

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3. Power Quality Issue and Problem Formulation
The rapid change in the electric load profile from being mainly a linear type to greatly

nonlinear, has created continued power quality problems which are difficult to detect

and is in general complex. The most important contributor to power quality problems is

the customers’ (or end-user electric loads) use of sensitive type nonlinear load in all

sectors (Industrial, Commercial and Residential).

Power Quality issues can be roughly broken into a number of sub-categories:

    Harmonics (integral, sub, super and interharmonics)

    Voltage swells, sags, fluctuations, flicker and Transients

    Voltage magnitude and frequency, voltage imbalance

    Hot grounding loops and ground potential rise (GPR)

    Monitoring and measurement of quasi-dynamic, quasi-static and transient

type phenomena.

Nonlinear type loads contribute to the degradation in the electric supply’s Power Quality

through the generation of harmonics. The increased use of nonlinear loads makes the

harmonic issue (waveform distortion) a top priority for all equipment manufacturers,

users and electric utilities. Severe Power System harmonics are usually the steady state

problem not the transient or intermittent type, and these harmonics can be mitigated by

using the new family of modulated/switched power filters.

Lower       order   harmonics      cause   the     greatest   concern     in   the   electrical

distribution/utilization system.     Harmonics interfere with sensitive -type electronic

communications and networks. Low order triplen harmonics cause hot-neutrals,

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grounding potential rise (GPR), light flickering, malfunction of computerized data

processing equipment and computer ne tworks and computer equipment.

There are several defined measures commonly used for indicating the harmonic

severity and content of a waveform. One of the most common measures is total

harmonic distortion in current (THD ) i .

            
   I    2
n   
THDi   

n2       ;

I1
             

             

Where I 1 : Fundamental (60Hz) Current; n: Harmonic order and I n : Harmonic current.

4. Total Harmonic Distortion (THD) and Power Factor (PF)

The power factor PF for any non-sinusoidal quantities is defined by:

VS I S 1 cos1 I S 1
PF                        cos1
VS I S      IS

I S 1 is the rms value of the fundamental 60Hz component of the current. The

displacement power factor (DPF, which is the same as the power factor in linear

circuits with pure sinusoidal voltage and current) is defined as the cosine of the

angle  1 (angle between the fundamental-frequency (60Hz) current and voltage

waveforms) which could be written as: DPF  cos 1 , therefore, the power factor PF

with a nonsinusoidal current is:

I S1
PF          DPF
IS

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In terms of total harmonic current distortion (THD ) i , the PF and I S (the rms value of

the total current) could be written as:

1
PF                DPF                      (4.1)
1  THDi2

              
(4.2)
where               I S  I S 1 1  THD   i
2

From an examination of (4.1) and (4.2), we can conclude that the power factor value

decreases with any high current harmonic content or distortion (THD ) i . These

definitions assume that the source voltage is near sinusoidal of fundamental

frequency (maximum allowable (THD )V =5%).

5. Power Quality Disturbances
In an electrical power system, there are various kinds of power quality disturbances.

They are classified into categories and their descriptions are important in order to

classify measurement results and to describe electromagnetic phenomena, which can

cause power quality problems. Some disturbances come from the supply network,

whereas others are produced by the load itself. The categories can be classified below

Short-duration voltage variations

   Long-duration voltage variations

   Transients

   Voltage imbalance

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    Waveform distortion

    Voltage fluctuation

    Power frequency variations

5.1 Short-Duration Voltage Variations
There are three types of short-duration voltage variations, namely, instantaneous,

momentary and temporary, depending on its duration. Short-duration voltage variations

are caused by fault conditions, energization of large loads, which require high starting

currents or loose connections in power wiring. Depending on the fault location and the

system conditions, the fault can generate sags, swells or interruptions. The fault

condition can be close to or remote from the point of interest. During the actual fault

condition, the effect of the voltage is of short-duration variation until protective devices

operate to clear the fault.

5.1.1     Sag
A sag (also known as dip) is a reduction to between 0.1 and 0.9 pu in rms voltage or

current at the power frequency for a short period of time from 0.5 cycles to 1 min. A

10% sag is considered an event during which the RMS voltage decreased by 10% to

0.9 pu. Voltage sags are widely recognized as among the most common and important

aspects of power quality problems affecting industrial and commercial customers. They

are particularly troublesome Since they occur randomly and are difficult to predict.

Voltage sags are normally associated with system faults on the distribution system,

sudden increase in system loads, lightning strikes or starting of large load like induction

motors. It is not possible to eliminate faults on a system. One of the most common

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causes of faults occurring on high-voltage transmission systems is a lightning strike.

When there is a fault caused by a lightning strike, the voltage can sag to 50% o f the

standard range and can last from four to seven cycles. Most loads will be tripped off

when encounter this type of voltage level. Possible effect of voltage sags would be

system shutdown or reduce efficiency and life span of electrical equipment, particularly

motors.

Equipment sensitivity to voltage sag occurs randomly and has become the most serious

power quality problem affecting many industries and commercial customers presently.

An industrial monitoring program determined an 87% of voltage disturbances could be

associated to voltage sags. Most of the faults on the utility transmission and distribution

system are single line-to-ground faults (SLGF).

5.1.2 Swell
A swell (also known as momentary overvoltage) is an increase in rms voltage or current

at the power frequency to between 1.1 and 1.8 pu for durations from 0.5 cycle to 1 min.

Swells are commonly caused by system fault conditions, switching off a large load or

energizing a large capacitor bank. A swell can occur during a single line-to-ground fault

(SLGF) with a temporary voltage rise on the unfaulted phases. They are not as common

as voltage sags and are characterized also by both the magnitude and duration. During

a fault condition, the severity of a voltage swell is very much dependent on the system

impedance, location of the fault and grounding. The effect of this type of disturbance

would be hardware failure in the equipment due to overheating.

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5.1.3 Interruption
An interruption occurs when there is a reduction of the supply voltage or load current to

less than 0.1 pu for duration not exceeding 1 min. Possible causes would be circuit

breakers responding to overload, lightning and faults. Interruptions are the result of

equipment failures, power system faults and control malfunctions. They are

characterized by their duration as the voltage magnitude is always less than 10% of the

nominal. The duration of an interruption can be irregular when due to equipment

malfunctions or loose connections. The duration of an interruption due to a fault on the

utility system is determined by the utility protective devices operating time.

5.2 Long-Duration Voltage Variations
Long-duration variations can be either overvoltages or undervoltages. They contain

root-mean-square (rms) deviations at power frequencies for a period of time longer than

1 min. They are usually not caused by system faults but system switching operations

and load variations on the system.

5.2.1 Overvoltage
An overvoltage is defined as an increase in the rms ac voltage greater than 110% at the

power frequency for duration longer than 1 min. Overvoltages can be the result of

switching off a large load, energizing a capacitor bank or incorrect tap settings on

transformers. These occur mainly because either the voltage controls are inadequate or

the system is too weak for voltage regulation. Possible effect could be hardware failure

in the equipment due to overheating.

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5.2.2 Undervoltage
An undervoltage (also known as brownout) is defined as a decrease in the rms ac voltage to

less than 90% at the power frequency for a period of tim e greater than 1 min. Undervoltage

is the result of switching on a load, a capacitor bank switching off or overloaded circuits.

Possible effect include system shutdown.     Most electronic controls are very sensitive as

compared to electromechanical devices, which tend to be more tolerant.

5.3 Transients
Transients can be classified into two categories, namely, impulsive and oscillatory.

These terms reflect the wave shape of a current or voltage transient.

5.3.1 Impulsive Transient
An impulsive transient is defined as a sudden, non-power frequency change in the

steady-state condition of voltage, current, or both, which is unidirectional in polarity

(either positive or negative). Impulsive transients are usually measured by their rise and

decay times and also their main frequency. Lightning is the most common cause of

impulsive transients. The shape of impulsive transients can be changed quickly by

circuit components and may have different characteristics when viewed from different

parts of the power system when high frequencies are involved. Impulsive transients can

even stimulate the natural frequency of power system circuits and produce oscillatory

transients.

5.3.2    Oscillatory Transient
An oscillatory transient describes as a sudden, non-power frequency change in the

steady-state condition of voltage, current, or both, which includes positive and negative

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polarity values. It consists of a voltage or current whose instantaneous value changes

polarity rapidly. They are characterized by its duration, magnitude and main frequency.

A back-to-back capacitor energization result in oscillatory transient currents is termed a

medium frequency transient. Medium frequency transients can also be the result of a

system response to an impulsive transient. Depending on the type of loads, worst case

could cause voltage spikes that break insulation somewhere in the system.

Capacitor switching, which associated with transient, is a daily utility operation to correct

the power factor. Many heavy industrial loads such as induction motors and furnaces

operate at low power factor. Heavy inductive loads cause excess current to flow in the

lines, which increase losses. The effects include equipment damage or failure, process

equipment shutdown and computer network problems.

Installation of capacitor banks can save energy and improve on the system security. A

reduction in power loss and an improved voltage profile can be achieved when

capacitors are dynamically controlled to changes in the feeder’s load. These benefits

depend on how capacitors are sized, placed and in controlled so that savings are

maximized.

In general, the total capacity of capacitor banks is approximately 50% of the total

generating capacity in a typical power distribution system. The factors that affect the

transient magnitude and characteristics are source strength, transmission lines, other

transmission system capacitor banks and switching devices. Pre-insertion resistors and

synchronous closing are some of the techniques that involved in the reduction of

capacitor switching transients.

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The capacitor voltage is not possible to change instantaneously when energization of a

capacitor bank occurs. This results in a sudden drop of system voltage towards zero,

followed by a fast voltage overshoot and finally an oscillating transient voltage imposed

on the 50Hz waveform. Depending on the instantaneous system voltage at the moment

of switching, the peak voltage magnitude can reach two times the normal system peak

voltage under severe conditions. Typical distribution system overvoltages due to

capacitor switching range from 1.1 - 1.6 pu with transient frequency ranging from 300 –

1 kHz.

Oscillatory transients with frequencies less than 300 Hz can also be found on the

distribution system. They are associated with ferroresonance and transformer

energization. Some common methods to limit transient overvoltages on the DC bus of

sensitive equipments are:

   Arrange a reactor in series with AC input terminal.

   Use of static var com pensators (SVCs) in the distribution systems.

5.4 Voltage Imbalance
Voltage imbalance (or unbalance) is a condition in which the maximum deviation from

the average of the three-phase voltages or currents, divided by the average of the

three-phase voltages or currents, expressed in percentage. Voltage imbalance can be

the result of blown fuses in one phase of a three -phase capacitor bank. Severe voltage

imbalance greater than 5% can cause damage to sensitive equipments.

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5.5 Waveform Distortion
Waveform distortion is a condition whereby a steady-state deviates from an ideal sine

wave of power frequency characterized by the main frequency of the deviation. There

are generally five types of waveform distortion, namely, dc offset, harmonics,

interharmonics, notching and noise.

5.5.1 DC Offset
DC offset is the presence of a dc current or voltage in an ac power system. This can

occur due to the effect of half-wave rectification. Direct current found in alternating

current networks can have a harmful effect. This can cause additional heating and

destroy the transformer.

5.5.2 Harmonic
Harmonics are a growing problem for both electricity suppliers and users. A harmonic is

defined as a sinusoidal component of a periodic wave or quantity having a frequency

that is an integral multiple of the fundamental frequency usually 50Hz or 60Hz.

Harmonic refers to both current and voltage harmonics. Harmonic voltages occur as a

result of current harmonics, which are created by electronic loads. These nonlinear

loads will draw a distorted current waveform from the supply system. The amount of

current distortion is dependent upon the kVA rating of the load, the types of load and the

fault level of the power system at the poi nt where the load is connected.

Industrial loads like electric arc furnaces, and discharge lighting can cause harmonic

distortion. The effect of harmonics in the power system includes the corruption and loss

of data, overheating or damage to sensitive equipment and overloading of capacitor

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banks. The high frequency harmonics may also cause interference to nearby

telecommunication system.

Fourier analysis can be used to describe distortion in terms of fundamental frequency

and harmonic components from a given distorted periodic waveform. By using this

technique, we can consider each component of the distorted wave separately and apply

superposition.    Using the Fourier series expansion, we can represent a distorted

periodic waveshape by its fundamental and harmonic: It is also common to use a single

quantity, the Total Harmonic Distortion (THD) as a measure of the effective value of

harmonic distortion. The development of Current Distortion Limits is to:

                                                          umer so that they will not

cause unacceptable voltage distortion levels for normal system characteristics.


utility.

The harmonic distortion caused by each single consumer s hould be limited to an

acceptable level and the whole system should be operated without existing harmonic

distortion. The harmonic distortion limits recommended here provide the maximum

allowable current distortion for a consumer.

5.5.3 Interharmonics
Interharmonics are defined as voltages or currents having frequency components that

are not integer multiples of the frequency at which the supply system is designed to

operate. The causes include induction motors, static frequency converters and arcing

devices. The effects of interharmonics are not well known.

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5.5.4 Notching
A periodic voltage disturbance caused by normal operation of power electronics devices

when current is commutated from one phase to another is termed notching. Notching

tends to occur continuously and can be characterized through the harmonic spectrum of

the affected voltage. The frequency components can be quite high and may not be able

to describe with measurement equipment used for harmonic analysis.

5.5.5 Noise

Noise is unwanted distortion of the electrical power signals with high frequency

waveform superimposed on the fundamental. Noise is a common source by

electromagnetic interference (EMI) or radio frequency interference (RFI), power

electronic devices, switching power supplies and control circuits. Noise disturbs

electronic devices such as microcomputer and programmable controllers. Use of filters

and isolation transformers can usually solve the problem.

5.6 Voltage Fluctuation
Voltage fluctuation is defined as the random variations of the voltage envelope where

the magnitude does not exceed the voltage ranges of 0.9 to 1.1 pu. Flicker usually

associates with loads that display continuous variations in the load current magnitude

causing voltage variations. The flicker signal is measured by its rms magnitude

expressed as a percent of the fundamental whereas voltage flicker is measured with

respect to the sensitivity of human eye. It is possible for lamp to flicker if the magnitudes

are as low as 0.5% and the frequencies are in the range of 6 to 8 Hz. One common

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cause of voltage fluctuations on utility transmission and distribution system is the arc

furnace.

5.7 Power Frequency Variations
Any deviation of the power system fundamental frequency from its nominal value (usually 50 or

60 Hz) is defined as power frequency variations. The power system frequency is associated with

the rotational speed of the generators supplying the system. The size and duration of the

frequency shift depends on the load characteristics and the response of the generation control

system to load changes. As the load and generation changes, small variations in frequency occur.

Frequency variations can be the cause of faults on power transmission system, large

load being disconnected or a large source of generation going off-line. Frequency

variations usually occur for loads that are supplied by a generator isolated from the

utility system. The response to sudden load changes may not be sufficient to adjust

within the narrow bandwidth required by frequency sensitive equipment. Possible effect

could result in data loss, system crashes and equipment damage.

6. Reactive Power Problems
Reactive power problems usually occur at the interconnection points of different

systems or now in the deregulated market between different owners of transmission or

distribution networks, reactive power generators and consumers. As reactive power is a

local product its value to system security and voltage control very much depends on the

location in the system.

The existence of embedded generation can release capacity in a distribution or other

network to which it is connected. And any generation embedded on that network

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reduces the likelihood of overloading and loss of supply, so improving the reliability of

the network.

Wind power stations is a common example of embedded generation. A specific

character of those power stations is that while generating the active power they

consume the reactive one. Combined with the generation level that varies with the

weather conditions, this causes voltage problems at the interconnection points and the

installment of compensation devices is required.

6.1 Reactive Power Sources
Reactive power is produced or absorbed by all major components of a power system:

              ;



   Power factor Corrections

6.1.1 Generators
Electric power generators are installed to supply active power. Additionally a generator

is supporting the voltage, producing reactive power when over-excited and absorbing

reactive power when under-excited. Reactive power is continuously controllable. The

ability of a generator to provide reactive support depends on its real-power production.

Like most electric equipment, generators are limited by their current-carrying capability.

Reactive power production is depended on the field heating limit and absorption on the

core end-heating limit of the generator. Active power output limit is limited by armature

heating. Control over the reactive output and the terminal voltage of the generator is

provided by adjusting the DC current in the generator’s rotating field. Control can be

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automatic, continuous, and fast. The inherent characteristics of the generator help

maintain system voltage. At any given field setting, the generator has a specific terminal

voltage it is attempting to hold. If the system voltage declines, the generator will inject

reactive power into the power system, tending to raise system voltage. If the system

voltage rises, the reactive output of the generator will drop, and ultimately reactive

power will flow into the generator, tending to lower system voltage. The voltage

regulator will accentuate this behavior by driving the field current in the appropriate

direction to obtain the desired system voltage.

6.1.2     Power transfer components
The major power transfer components are transformers, overhead lines and underground

cables. HVDC converter stations can also be treated as power transfer components.

6.1.2.1    Transformers

Transformers provide the capability to raise alternating -current generation voltages to

levels that make long-distance power transfers practical and then lowering voltages

back to levels that can be distributed and used. The ratio of the number of turns in the

primary to the number of turns in the secondary coil determines the ratio of the primary

voltage to the secondary voltage. By tapping the primary or secondary coil at various

points, the ratio between the primary and secondary voltage can be adjusted.

Transformer taps can be either fixed or adjustable under load through the use of a load-

tap changer (LTC). Tap capability is selected for each application during transformer

design. Fixed or variable taps often provide ±10% voltage selection, with fixed taps

typically in 5 steps and variable taps in 32 steps. Transformer-tap changers can be used

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for voltage control, but the control differs from that provided by reactive sources.

Transformer taps can force voltage up (or down) on one side of a transformer, but it is

at the expense of reducing (or raising) the voltage on the other side. The reactive power

required to raise (or lower) voltage on a bus is forced to flow through the transformer

from the bus on the other side. The reactive power consumption of a transformer at

rated current is within the range 0.05 to 0.2 p.u. based on the transformer ratings. Fixed

taps are useful when compensating for load growth and other long-term shifts in system

use. LTCs are used for more-rapid adjustments, such as compensating for the voltage

fluctuations associated with the daily load cycle. While LTCs could potentially provide

rapid voltage control, their performance is normally intentionally degraded. With an LTC,

tap changing is accomplished by opening and closing contacts within the transformer’s

tapchanging mechanism.

6.1.2.2   Transmission lines and cables

Transmission lines and cables generate and consume reactive power at the same time.

The reactive power generation is almost constant, because the voltage of the line is

usually constant, and the line’s reactive power consumption depends on the current or

load connected to the line that is variable. So at the heavy load conditions transmission

lines consume reactive power, decreasing the line voltage, and in the low load

conditions – generate, increasing line voltage. The case when line’s reactive power

production is equal to consumption is called natural loading.

Page 23 of 58
6.1.2.3    HVDC converters

Thyristor-based HVDC converters always consume reactive power when in operation.

The reactive power consumption of the HVDC converter/inverter is 50-60 % of the

active power converted. The reactive power requirements of the converter and system

have to be met by providing appropriate reactive power in the station. For those reason

reactive power compensations devices are used together with reactive power control

from the ac side.

6.1.3 Loads
Voltage stability is closely related to load characteristics. The reactive power

consumption of the load has a great impact on voltage profile at the bus. The response

of loads to voltage changes occurring over many minutes can affect voltage stability.

For transient voltage stability the dynamic characteristics of loads such as induction

motors are critical. Some typical reactive power consuming loads examples are given

below.

6.1.3.1    Induction motors

About 60 % of electricity consumption goes to power motors and induction motors take

nearly 90 % of total motor energy depending on industry and other factors. The steady-

state active power drawn by motors is fairly independent of voltage until the point of

stalling. The reactive power of the motor is more sensitive to voltage levels. As voltage

drops the eactive power will decrease first, but then increase as the voltage drops

further.

Page 24 of 58
6.1.3.2   Induction generators

Induction generators as reactive power load became actual with the wind power station

expansion into electricity sector. Wind plants are equipped with induction generators,

which require a significant amount of reactive power. Part of the requirement is usually

supplied by local power factor correction capacitors, connected at the terminal of each

turbine. The rest is supplied from the network, which can lead to low voltages and

increased losses.

6.1.3.3   Discharged lightning

About one-third of commercial load is lightning – largely fluorescent. Fluorescent and

other discharged lightning has a voltage sensitivity Pv in the range 1-1.3 and Qv in the

range 3- 4.5. At voltages between 65-80 % of nominal they will extinguish, but restart

when voltage recovers.

6.1.3.4   Constant energy loads

Loads such as space heating, water heating, industrial process heating and air

conditioning are controlled by thermostats, causing the loads to be constant energy in

the time scale of minutes. Heating loads are especially important during wintertime,

when system load is large and any supply voltage drop causes an increase in load

current, that makes situation even worse.

Page 25 of 58
6.1.3.5   Arc furnaces

Arc furnaces are a unique representation of problems with voltage stability, power factor

correction and harmonic filtering. Rapid, large and erratic variations in furnace current

cause voltage disturbances for supply utility and nuisance to neighboring customers. So the

problem of voltage stabilization and reactive power control is usually solved by connecting

the furnace to a higher network voltage, installing synchronous condensers and other fast

responding reactive power generating units.

6.1.4 Reactive Power compensation devices

6.1.4.1   Synchronous condensers

Every synchronous machine (motor or generator) has the reactive po wer capabilities

the same as synchronous generators. Synchronous machines that are designed

exclusively   to   provide   reactive   support are      called   synchronous   condensers.

Synchronous condensers have all of the response speed and controllability advantages

of generators without the need to construct the rest of the power plant (e.g., fuel-

handling equipment and boilers). Because they are rotating machines with moving parts

and auxiliary systems, they require significantly more maintenance than static

compensators. They also consume real power equal to about 3% of the machine’s

reactive-power rating. Synchronous condensers are used in transmission systems: at

the receiving end of long transmissions, in important substations and in conjunction with

HVDC converter stations.

Small synchronous condensers have also been used in high-power industrial networks

to increase the short circuit power. The reactive power output is continuously

Page 26 of 58
controllable. The response time with closedloop voltage control is from a few seconds

and up, depending on different factors.

In recent years the synchronous condensers have been practically ruled out by the

thyristor controlled static VAR compensators, because those are much more cheaper

and have regulating characteristics similar to synchronous condensers.

6.1.4.2   Static VAR compensators

An SVC combines conventional capacitors and inductors with fast switching capability.

Switching takes place in the sub cycle timeframe (i.e., in less than 1/50 of a second),

providing a continuous range of control. The range can be designed to span from

absorbing to generating reactive power. Advantages include fast, precise regulation of

voltage and unrestricted, largely transient-free, capacitor bank switching. Voltage is

regulated according to a slope characteristic.

Static VAR compensator could be made up from:
1. TCR (thyristor controlled reactor);
2. TSC (thyristor switched capacitor);
3. TSR (thyristor switched reactor);
4. FC (fixed capacitor);

6.1.4.3   Harmonic filter

Because SVCs use capacitors they suffer from the same degradation in reactive

capability as voltage drops. They also do not have the short-term overload capability of

generators and synchronous condensers. SVC applications usually require harmonic

filters to reduce the amount of harmonics injected into the power system by the thyristor

switching. SVCs provide direct control of voltage; this is very valuable when there is little

Page 27 of 58
generation in the load area. The remaining capacitive capability of an SVC is a good

indication of proximity to voltage instability. SVCs provide rapid control of temporary

overvoltages. But on the other hand SVCs have limited overload capability, because

SVC is a capacitor bank at its boost limit. The critical or collapse voltage becomes the

SVC regulated voltage and instability usually occurs once an SVC reaches its boost

limit. SVCs are expensive; shunt capacitor banks should first be used to allow unity

power factor operation of nearby generators.

6.1.4.4   Static synchronous compensator (STATCOM)

The STATCOM is a solid-state shunt device that generates or absorbs reactive power

and is one member of a family of devices known as flexible AC transmission system

(FACTS) devices. The STATCOM is similar to the SVC in response speed, control

capabilities, and the use of power electronics. Rather than using conventional

capacitors and inductors combined with thyristors, the STATCOM uses self-

commutated power electronics to synthesize the reactive power output. Consequently,

output capability is generally symmetric, providing as much capability for production as

absorption. The solid-state nature of the STATCOM means that, similar to the SVC, the

controls can be designed to provide very fast and effective voltage control.

While not having the short-term overload capability of generators and synchronous

condensers, STATCOM capacity does not suffer as seriously as SVCs and capacitors

do from degraded voltage. STATCOMs are current limited so their MVAR capability

responds linearly to voltage as opposed to the voltage-squared relationship of SVCs

and capacitors. This attribute greatly increases the usefulness of STATCOMs in

preventing voltage collapse.

Page 28 of 58
6.1.4.5    Series capacitors and reactors

Series capacitors compensation is usually applied for long transmission lines and

transient stability improvement. Series compensation reduces net transmission line

inductive reactance. The reactive generation I2XC compensates for the reactive

consumption I2X of the transmission line. Series capacitor reactive generation

increases with the current squared, thus generating reactive power when it is most

needed. This is a self-regulating nature of series capacitors. At light loads series

capacitors have little effect.

6.1.4.6    Shunt capacitors

The primary purposes of transmission system shunt compensation near load areas are

voltage control and load stabilization. Mechanically switched shunt capacitor banks are

installed at major substations in load areas for producing reactive power and keeping

voltage within required limits. For voltage stability shunt capacitor banks are very useful

in allowing nearby generators to operate near unity power factor. This maximizes fast

acting reactive reserve. Compared to SVCs, mechanically switched capacitor banks

have the advantage of much lower cost. Switching speeds can be quite fast. Current

limiting reactors are used to minimize switching transients.

There are several disadvantages to mechanically switched capacitors. For voltage

emergencies the shortcoming of shunt capacitor banks is that the reactive power output

drops with the voltage squared. For transient voltage instability the switching may not be

fast enough to prevent induction motor stalling. Precise and rapid control of voltage is

not possible. Like inductors, capacitor banks are discrete devices, but they are often

configured with several steps to provide a limited amount of variable control. If voltage

Page 29 of 58
collapse results in a system, the stable parts of the system may experience damaging

overvoltages immediately following separation.

6.1.4.7      Shunt reactors

Shunt reactors are mainly used to keep the voltage down, by absorbing the reactive

power, in the case of light load and load rejection, and to compensate the capacitive

load of the line.

6.1.5 Why Power Factor Correction

   Increased source efficiency
- lower losses on source impedance
- lower voltage distortion (cross-coupling)
- higher power available from a given source

   Reduced low-frequency harmonic pollution

   Compliance with limiting standards (IEC 555-2, IEEE 519 etc.)

6.1.5.1     Power Factor Correction Techniques

     PASSIVE METHODS: LC filters
o Power factor not very high
o Bulky components
o High reliability
o Suitable for very small or high power levels

     ACTIVE METHODS: high-frequency converters
o High power factor (approaching unity)
o Possibility to introduce a high-frequency insulating transformer layout
dependent high-frequency harmonics generation (EMI problems)
o Suitable for small and medium power levels

Page 30 of 58
7. Software
In most cases, specialized software tools make use of intelligent techniques to

computerize the power quality evaluations for improved accuracy and efficiency, as

manual analysis may be too difficult to carry out due to lack of time and special

knowledge. There have been an increasing number of simulation tools suitable for

transient analysis in the last few years. Besides the well-known EMTP and its variants

ATP, MATLAB, and the PSCAD / EMTDC.

In this course, both the MATLAB and PSCAD/EMTDC software have been used for

analyzing power systems disturbances.

8.    Digital Simulation Models

Grid electricity is generally distributed as three phase balanced voltage waveforms

forming the common 3-phase sinusoidal AC system. One of the characteristics of the

AC system is its sinusoidal voltage waveforms, which must always remain as close as

possible to that of a pure sine-wave. If it is distorted beyond certain acceptable limits, as

is often the case on power source networks comprising nonlinear type loads, the supply

waveform must be cleaned and corrected. The distorted waveform is usually composed

of a number of dominant sine waves of different harmonic frequencies, including the

fundamental one at the 60Hz power frequency, referred as the fundamental frequency,

and the rest is referred to as the “integral harmonic ripple component” with frequencies

which are multiple of that of the fundamental. Harmonic effective quantities are

generally expressed in terms of their RMS-value since the heating or loss effect

depends on this total sum squared value of the distorted waveform.

Page 31 of 58
8.1 System Models

Figure 8.1 depicts the single line diagram of radial utilization system feeding a nonlinear

type load. The load bus is connected to the switched/modulated Smart Power Filter

(SMPF). SMPF can be used to improve electric supply power quality by reducing

harmonic content in supply current by minimizing waveform distortion, notching and

voltage fluctuations (swell, sag). Rs and Ls represent the equivalent source transformer

feeder resistance and inductance. V S and V L represent the supply and load voltage

respectively.
Electric
System+Transformer+Feeder             Equivalent
Utility
(Plant) Load

Load Bus
Vs              Rs       Ls            VL

Nonlinear Load (NLL)
   Conv erter Ty pe
Switched/Modulated               Arc Ty pe
Power Filter or Static           Dy namic
Capacitor Compensator             Cy clical
* Smart-controllers are
   Ripple
based on specif ied control
   Inrush
objectiv es             YF(s)                                  Temporal
SMPF             N       Motorized on/of f
Control                                                 L
is
Signals                                                 L
Smart                on/of f or
Vs                Controller             PWM            Nonlinear
Ps                   *
Load

Figure 8.1: Single Line Diagram of Radial Utilization System

Page 32 of 58
8.1.1 CASES # 1 TO # 5

CASE # 1
Case # 1 addresses the power quality enhancement scheme using modulated power

filter compensator. The modulated power filter is developed by Dr. Sharaf. The use of

the switched modulated power filter compensator is to enhance power quality in low

voltage distribution systems under unbalanced and fault conditions. The simulation

results are shown in Appendix A and are done with and without the modulated power

compensating filter. The software used in this case is the Matlab/Simulink.

The complete system model is depicted in Appendix A. The Modulated power filter is

controlled by a dynamic tri-loop controller. The purpose of this dynamic controller is to

minimize switching transients, maximize power/energy utilization and to improve power

factor under unbalanced load and fault conditions. The major components of the AC

system are: Three phase-four wire AC power supplies; Novel Modulated power Filter;

Tri -loop dynamic error driven error controller and Single phase load.

CASE # 2
Case # 2 addresses another power quality enhancement scheme also using modulated

power filter compensator. The modulated power filter is developed by Dr. Sharaf. This

case presents a novel dynamic voltage regulator Power filter and capacitor correction

compensator     scheme to enhance power utilization and improve power quality in low

voltage distribution systems under the nonlinear load conditions. The modulated power

filter is controlled by a dynamic tri-loop error driven PID controller. The purpose of this

dynamic hybrid Tri-functional compensator is to minimize feeder switching transients,

Page 33 of 58
maximize power/energy utilization and to improve power factor under unbalanced load

and fault conditions. The functional MATLAB/SIMULINK model of a radial distribution

system with the proposed dynamic hybrid reactive power compensation scheme is

presented as shown in Appendix B.

CASE # 3
Case # 3 illustrates the use of a STATCOM to provide active filtering for the ac side of a

6-pulse converter system. The Active filter is connected through a 20 kVA, Y-Y

transformer to a 200 V, 50 Hz, 3-Phase bus, with a 6-pulse converter load

The simulation results are shown in Appendix C and are done with and without the

compensating filter. Graphs show clearly the difference in harmonic contents in the

supply current and demonstrate the Power quality improvement and the efficiency of the

compensating filter. The software used in this case is the PSCAD.

CASE # 4
Case # 4 illustrates the power quality problem of Tingle Voltage; the problem was that

farm animals, during winter months, were experiencing a "tingle voltage", due to

suspected poor grounding on the local ground grid.

By using PSCAD, the local system is simulated and determined that the grounding

problem was at least partially related to ground rod resistance. During the winter

months, the ground conductivity is poor, resulting in a poor connection between the

ground rods and earth.

Page 34 of 58
The simulation results are shown in Appendix D and are done by varying the ground

resistor. Graphs show clearly the difference in voltage affecting the cows. By varying the

ground resistance, the voltage varies and affects the cows.

CASE # 5
Case # 5 illustrates the use of a 12-Pulse STATCOM for Reactive power control. The

STATCOM is a solid-state shunt device that generates or absorbs reactive power and is

one member of a family of devices known as flexible AC transmission system (FACTS)

devices. The STATCOM is similar to the SVC in response speed, control capabilities,

and the use of power electronics. Rather than using conventional capacitors and

inductors combined with thyristors, the STATCOM uses self-commutated power

electronics to synthesize the reactive power output. Consequently, output capability is

generally symmetric, providing as much capability for production as absorption. The

solid-state nature of the STATCOM means that, similar to the SVC, the controls can be

designed to provide very fast and effective voltage control.

The simulation results are shown in Appendix E and the control is designed to provide

very fast and effective voltage control. The software used in this case is the PSCAD.

Page 35 of 58
REFERENCES

[1]   A. M. Sharaf and M. A. Habli, “Demand Side Management and Energy
Conservation Using Switched Capacitor Compensation”, Proceedings of the
International Conference ICCCP01 Muscat, Oman, Feb 2001.

[2]   A. M. Sharaf, S Abu-Azab “Power Quality Enhancement of Time Dependent
Interharmonic Loads “ Proceedings of the Nonth International IEEE Conference
on Harmonics and Quality of Power ICHPS’2000, Orlando, FL, October 2000.

[3]   A.M. Sharaf, Caixia Guo, and Hong Huang. “A novel smart compensation for
energy/power quality enhancement of nonlinear loads”, Proceedings of the 1997
Canadian Conference on Electrical and Computer Engineering, CCECE, May 25-
28, 1997, St. John’s, Newfoundland, Canada.

[4]   W. Mack Grady, “Harmonics and how they relate to power factor”, Proceedings
of the EPRI Power Quality Issues and Opportunities Conference, San Diego, CA,
November 1993.

[5]   A.M. Sharaf, Pierre Kreidi, ”Dynamic compensation using switched/modulated
power filters, ” Proceedings of the IEEE Canadian Conference on Electrical
and Computer Engineering CCECE 2002, Winnipeg, Manitoba, Canada, May 12-
15, 2002

[6]   A.M. Sharaf, Pierre Kreidi, ”Power quality enhancement and        harmonic
th
reduction   using    dynamic power filters,” 7 International Conference on
Modeling and Simulation of Electric Machines, Converters and Systems.
ELECTRIMACS 2002. Montreal, Quebec, Canada, August 18-21, 2002.

[7]   A.M. Sharaf, Pierre Kreidi, ”Power quality enhancement and harmonic
compensation scheme for asymmetrical nonlinear loads”, 10 th International
Power Electronics and Motion Control Conference. EPE-PEMC 2002 Cavtat &
Dubrovnik, Croatia, September 9-11, 2002.

[8]   A.M. Sharaf, Pierre Kreidi, ”Power quality enhancement using a unified
compensator and switched filter”, International Conference on Renewable
Energy and Power Quality-ICREPQ’2003, Vigo-Spain, April 9-11, 2003

[9]   A.M. Sharaf, Pierre Kreidi, ”Power quality enhancement using a unified switched
capacitor compensator,” Proceedings of the IEEE Canadian Conference on
Electrical and Computer Engineering CCECE 2003, Montreal, Quebec, Canada,
May 4-7, 2003

Page 36 of 58
[10]   A.M. Sharaf, Wei Wu, “A Novel Power Quality Enhancement Scheme In Low
Volatge Distribution System Using Modulated Power Filter Compensator”.

[11]   A.M. Sharaf, Ting Zhang, “Novel Power Quality Enhancement Scheme Using
Modulated Power Filter Compensator”

[12]   Valery Knyazkin, “Technical Report – The Oxelösund Case Study”, A-EES-0010,
August 2000.

[13]   MC. Ryan et al., “Power Quality reference guide”, Ontario Hydro Publications. 2 nd
edition, 1990.

[14]   RC Dugan, M.F. McGranaghan, H.W. Beaty, “Electrical Power Systems Quality”,
McGraw Hill, 1996, ISBN 0-07-018031-8.

[15]   Peter Axelberg et al., “Current and Emerging Trends in IEC Standards and Their
Implications for Power quality Measurement Systems”, Electrical Distribution and
Transmission PTY LTD Publications, 2001.

[16]   Electrical Business Magazine, December 2001. The Authoritative voice of
Canada’s electrical industry. Kerwil Publications.

[17]   EPRI and CEIDS Team, “The Power Quality Implications of Conservation
Voltage Reduction”, EPRI Publications – PQ Commentary Number 4, December
2001.

[18]   K Srinivasan, R. Jutras, T.D. Nguyen, “Sharing steady state power quality
deterioration between customer and utility sides”, Power Quality Applications
1997 Europe, Stockholm, June1997.

[19]   Owyong Leng, “Simulating Power Quality Problems”, BS Thesis, University of
Queensland, Australia, 2001.

[20]   National Electrical Code Internet Connection, “Case Studies”,
http://www.neccode.com/studies/harmonic.htm.

[21]   Pierre Kreidi “Electric Power Quality, Harmonic Reduction and Power/Energy
Saving Using Modulated Power Filters and Capacitor Compensators” Thesis ,
UNB 2003.

Page 37 of 58
APPENDIX ‘A’                                                                                                                                          CASE # 1

NLL _A

In    N
aA                                                       aA
a
A                                         A               A
b                                                                                                                                                                        NLL _B
bB                   B               B                   bB
B       c
C               C                                                                                                                           N
C       n            cC                                                       cC                                                                                                 In
1 km Feeder
25 kv/600 v
Transformer Bus                                         Load Bus
400 kVA                                                                                                                                                                          NLL _C

A

B

C
MPFC
A

B

C

In   N

Cn
s1

s2

C
A

B
25 KV AC source                                                                                             s1

C
B
A

C
Linear Load
[In ]     -K-            In                                                                   Three -Phase Fault
PWM
s2

Controller

[In ]
Continuous
Goto
i   +
powergui                                                                                                      -
Current Measurement
Zn                                                                             +
v                [Vn]
-
Rg

[Vn]                                            VL                            V
From 3
[In ]                                            IL                           I
Scope 2
From 2                                                                         Load

In
In
Nutral Harmonic
Load Harmonic

Matlab- Simulink functional model of the 3Phase-4 Wire Model

Ei                      Et
1                      r
signal ms                                                                             0.8
sigma 1         sigma 2
In
Irms                                                                            Gama I

1
Delay 1                                                                                                                                 Pulses                           s1
PID                        Signal(s)
0.15                                          1.8                                                                                                        2
Saturation                                            s2
I1 ref                                       Gama n                                                              PWM Generator

En

1
|u|                    1.2
0.001 s+1                                                                                                         rEh
Transfer Fcn 2                                          Abs                    Gama h

Tri loop dynamic Variable structure -sliding mode control Scheme

Page 38 of 58
2       B

1   A                                         3   C

C
A

B
Cf

C
A

B
A

B

C
+

-
1            g
2
s1
1
Rf
S1

Lf

2
s2        g
2
1
S2

4   Cn

Modulated Power Filter Compensator Scheme

Converter type nonlinear load model

Page 39 of 58
Without Filter Compensation                                                                    With Filter Compensation

power factor @ phase A                                                                                 power factor @ phase A
1
0.5
0.8
0
0.6
-0.5
0   0.1             0.2                     0.3   0.4           0.5                            0       0.05     0.1          0.15           0.2         0.25         0.3       0.35

power factor @ phase B                                                                                 power factor @ phase B
1
1
0.5

0                                                                                             0.5
0   0.1             0.2                     0.3   0.4           0.5                            0       0.05     0.1          0.15           0.2         0.25         0.3       0.35

power factor @ phase C                                                                                 power factor @ phase C
1

0.5
1

0                                                                                             0.8

-0.5                                                                                            0.6
0   0.1             0.2                     0.3   0.4           0.5
Time (s)                                                            0       0.05     0.1          0.15         0.2           0.25         0.3       0.35
Time (s)

Load Power Factor

Load Current (rms)/pu @ phase A                                                                           Load Current (rms)/pu @ phase A
1.5                                                                                                   1

1
0.5
0.5
0
0                                                                                                       0      0.5         1             1.5             2          2.5         3             3.5
0         0.1                         0.2               0.3     0.36                                                                                                                     4
x 10
Load Current (rms)/pu @ phase B                                                                           Load Current (rms)/pu @ phase B
1                                                                                              0.4

0.5                                                                                              0.2

0                                                                                                   0
0      0.5         1             1.5             2          2.5         3             3.5
0         0.1                         0.2               0.3     0.36
4
x 10
Load Current (rms)/pu @ phase C                                                                           Load Current (rms)/pu @ phase C
1                                                                                              0.4

0.5                                                                                              0.2

0                                                                                                   0
0         0.1                         0.2               0.3     0.36                               0      0.5         1             1.5             2          2.5         3             3.5
Time (s)                                                                                                       Time(s)                                        4
x 10

Load Current

Page 40 of 58
Load Voltage (rms)/pu @ phase A                                                                               Load Voltage (rms)/pu @ phase A
1                                                                                           1.5

0.5                                                                                              1

0.5
0
0    0.1        0.2               0.3         0.4    0.5
0
0          0.5         1            1.5               2      2.5         3      3.5
Load Voltage (rms)/pu @ phase B                                                                                                                                   4
x 10
1                                                                                                                            Load Voltage (rms)/pu @ phase B
1.5
0.5                                                                                              1

0                                                                                           0.5
0    0.1        0.2               0.3         0.4    0.5
0
Load Voltage (rms)/pu @ phase C                                                    0          0.5         1            1.5               2      2.5         3      3.5
1                                                                                                                                                                                 4
x 10
Load Voltage (rms)/pu @ phase C
0.5                                                                                              1

0                                                                                           0.5
0    0.1        0.2               0.3         0.4    0.5

Time (s)
0
0          0.5         1            1.5               2      2.5         3      3.5
Time (s)                              4
x 10

Load Voltage

Power/pu @ phase A                                                                                         Power/pu @ phase A

0.2                                                                                     0.2

0.1                                                                                     0.1
0
0           0.1        0.2                0.3          0.4     0.5                     0
0             0.05         0.1         0.15              0.2        0.25     0.3       0.35

Power/pu @ phase B
0.2                                                                                                                                 Power/pu @ phase B
0.2

0.1
0.1

0
0       0.1        0.2                0.3          0.4     0.5                     0
0             0.05         0.1         0.15              0.2        0.25     0.3       0.35

Power/pu @ phase C
0.2                                                                                                                                 Power/pu @ phase C
0.2
0.1
0.1
0
0       0.1        0.2                0.3          0.4     0.5
Time (s)                                                 0
0             0.05         0.1         0.15              0.02       0.25     0.3       0.35
Time (s)

Power

Page 41 of 58
S1

1

0.8

0.6

0.4

0.2

0
0.15                      0.2   0.25

S2

1

0.8

0.6

0.4

0.2

0
0.15                      0.2   0.25
Time(s)

Compensator S1 and S2

Page 42 of 58
APPENDIX ‘B’                                                                                                                                                    CASE # 2

I                                                            I                                       I

Transmission line                                                           V                                                            V                                       V
25kv 2km
Measurement 1                                                   Measurement 2                         Measurement 3
i
+    -                                                          i                                                         i
+   -                                                     +   -

1                            2

Load 1 2 MVA@PF=0.8                            + v Load 2 1 .5MVA@PF=0.8                                      + v
-                                                              -         Load 3 1 .5MVA @PF=0.8              + v
+ v                                                                                                                                                             -
-
Linear Transformer

138 kv             25 kv
Scope

I
I                                                 I

V
V
I                                                                      V
IL                                                                                                                                                        Measurement 5                                  Measurement 4
g            [S1]           Measurement 6
Harmonic Analysis               2
1
i   +
i                                                 i   +
i                                                                           i                                                                +                                                                           -
+                                                                           +                                                                                                         -
In                                                                                                                                                        -
-                                                                           -

N.L.Load                                                                        Controller                                                                                                                                           +
+                              v
[S2]                                                                                                                                                         v    -                                  -
+                                                                 Load 5 1 MVA@PF=0.8                load 4 1 MVA@PF=0.8
VL                                   v       -
[S1]                  PWM1                                                                                      Load 6 1 MVA@PF=0.8
IL                           Voltage Measurement 6
[IL ]
[S2]                  PWM2
PF
[PF]
g

1
2

Continuous

V6
powergui

Simulink model of the radial distribution system with the non- linear load

Ev
1                                                                                           1
1
V 1 ref                                                                                   Gama V                                                            Et                                                       PWM
PWM1
1
1                          rms
signal                           -K-
PID                                  Pulses
Signal(s)
VL                                                                                 0.02 s+1                                                                         Et
Gain 1                                                                                                                                                                                                    2
Vrms1                                                  Transfer Fcn 1                                                                                               Saturation                                                        PWM2
PWM Generator
3
PF

V1 ref 1 0.98

Epf
1
rms                                                                                                                   0.5
2                             signal                 K-                                         0.02 s+1
IL                          Vrms2                     Gain                                    Transfer Fcn 2                                           Gama P                rEp

Delay 2

Dynamic Tri-loop error driven PID controller

Page 43 of 58
V .I

i                                    I
Pulses
Signal(s)          g         +       +
-
V
PWM Generator                 Current Measurement 7
1                                                                  A         -                                             Measurement 7
In
Terminator                    1                 2                    Universal Bridge
+
v   -
Voltage Measurement 1

25 kV/0.8kV
Voltage Measurement
+ v
-

Converter type non-linear loads

Compensation Switching

Page 44 of 58
Without Filter Compensation                        With Filter Compensation

Current and voltage waveforms of the nonlinear load without and with compensation

Voltage waveforms of the linear load without and with compensation

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Voltage waveforms and P-Q profile without and with compensation

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APPENDIX ‘C’                  CASE # 3

WITHOUT COMPENSATING FILTER

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CASE # 3

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CASE # 3

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APPENDIX ‘C’                CASE # 3

WITH COMPENSATING FILTER

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CASE # 3

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CASE # 3

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APPENDIX ‘D’         CASE # 4

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APPENDIX ‘D’          CASE # 4

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APPENDIX ‘E’        CASE # 5

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CASE # 5

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APPENDIX ‘E’          CASE # 5

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CASE # 5

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